JP2000145547A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the emission of soot, NOx and unburnt hydrocarbon simultaneously and prevent excessive rises in catalyst temperature at the same time. SOLUTION: A larger amount of EGR gas than the amount thereof that results in the peak generation of soot is fed to a combustion chamber 5 to offer low-temperature combustion with almost no generation of soot or no emission of not only soot but NOx. A catalyst 25 with an oxidizing function is arranged in an exhaust pipe 28 to prevent the emission of unburnt hydrocarbon. When the temperature of the catalyst 25 becomes not less than a preset temperature during low-temperature combustion, the low-temperature combustion is cancelled or the air-fuel ratio is shifted to the lean side, so that a reduced amount of unburnt hydrocarbon flowing into the catalyst 25 decreases the generation of heat of reaction and thus prevents excessive rises in temperature of the catalyst 25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine, for example, a diesel engine, an engine exhaust passage and an engine intake passage are connected by an exhaust gas recirculation (hereinafter referred to as EGR) passage in order to suppress the generation of NOx. Exhaust gas, that is, EGR gas, is recirculated through the passage into the engine intake passage. In this case, the EGR gas has a relatively high specific heat, and therefore can absorb a large amount of heat.
The combustion temperature in the combustion chamber decreases as the GR gas amount increases, that is, as the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)) increases. When the combustion temperature decreases, the amount of generated NOx decreases. Therefore, the higher the EGR rate, the lower the amount of generated NOx.

As described above, it has been known that the amount of generated NOx can be reduced by increasing the EGR rate. However, when the EGR rate is increased, the soot generation amount, that is, smoke, starts to increase rapidly when the EGR rate exceeds a certain limit. In this regard, it has conventionally been considered that if the EGR rate is further increased, the smoke will increase indefinitely. Therefore, the smoke starts to increase rapidly.
The GR rate is considered to be the maximum allowable limit of the EGR rate.

Therefore, conventionally, the EGR rate is set within a range not exceeding the maximum allowable limit. The maximum allowable EGR rate varies considerably depending on the type of engine and fuel, but is approximately 30 to 50%.
Therefore, in a conventional diesel engine, the EGR rate is at most 3
It is reduced from 0% to about 50%.

As described above, conventionally, it has been considered that the maximum allowable limit exists for the EGR rate.
If the R rate is within the range not exceeding this maximum allowable limit, NO
The amount of x and smoke was determined to be as small as possible. However, in this way EGR
Even if the rate is set so as to minimize the generation of NOx and smoke, there is a limit to the reduction of the generation of NOx and smoke, and in fact, a considerable amount of N
At present, Ox and smoke are generated.

However, if the EGR rate is made larger than the maximum allowable limit in the course of research on the combustion of a diesel engine, the smoke rapidly increases as described above. However, the amount of generated smoke has a peak, and the peak exceeds this peak. EGR
When the rate is further increased, the smoke starts to decrease rapidly, and when the EGR rate is increased to 70% or more during idling operation, and when the EGR gas is cooled strongly, the smoke is reduced when the EGR rate is increased to about 55% or more. It becomes almost zero. That is, it was found that soot was hardly generated. In this case, N
It has also been found that the amount of Ox generated is extremely small.
After that, the reason why no soot was generated was examined based on this finding, and as a result, unprecedented soot and NO
Thus, a new combustion system capable of simultaneously reducing x has been constructed. This new combustion system will be described in detail later, but in short, it is basically based on stopping the growth of hydrocarbons in the middle stage until the hydrocarbons grow into soot.

That is, as a result of repeated experimental studies, it has been found that when the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is lower than a certain temperature, the growth of hydrocarbons is stopped at a halfway stage before reaching soot. However, when the temperature of the fuel and the gas around it rises above a certain temperature, the hydrocarbons grow into soot at a stretch. In this case, the temperature of the fuel and the surrounding gas is greatly affected by the heat absorbing action of the gas around the fuel when the fuel is burned, and the amount of heat absorbed by the gas around the fuel is adjusted according to the calorific value at the time of burning the fuel. As a result, the temperature of the fuel and the surrounding gas can be controlled.

Accordingly, if the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, soot will not be generated, and the fuel during combustion in the combustion chamber and its surroundings will not be generated. Can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, by adjusting the amount of heat absorbed by the gas around the fuel. On the other hand, hydrocarbons whose growth has stopped halfway before reaching soot can be easily purified by post-treatment using an oxidation catalyst or the like. This is the basic idea of a new combustion system.

[0009]

However, a new combustion system as described above has not been disclosed yet. Therefore, the conventional combustion system already disclosed cannot exhibit new effects based on the new combustion system described above.

[0010] Accordingly, the present invention simultaneously prevents the emission of soot and NOx from the internal combustion engine while preventing the unburned hydrocarbons from being exhausted from the internal combustion engine. It is another object of the present invention to provide an internal combustion engine that can prevent the catalyst temperature from excessively rising.

[0011]

According to the first aspect of the present invention, as the amount of the inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak. When the amount of the inert gas supplied into the combustion chamber is further increased, the temperature of the fuel during combustion in the combustion chamber and the temperature of the surrounding gas become lower than the temperature at which soot is generated, and the soot is hardly generated. The engine is capable of performing combustion in which the amount of inert gas supplied into the combustion chamber is larger than the amount of inert gas at which the generation amount of soot becomes a peak, and soot is hardly generated, and A catalyst having an oxidizing function disposed in the engine exhaust passage for oxidizing the discharged unburned hydrocarbons; and a catalyst temperature detecting means for detecting a temperature of the catalyst, wherein the catalyst temperature is predetermined. Above the specified temperature , The internal combustion engine be prohibited from performing the combustion in which the soot is hardly generated is provided.

In the internal combustion engine according to the first aspect, the amount of the inert gas supplied into the combustion chamber is larger than the amount of the inert gas at which the generation amount of soot is a peak, and the combustion at which the soot is hardly generated is performed at a low temperature. Since it can be carried out below, it is possible to simultaneously prevent the emission of soot and the emission of NOx from the internal combustion engine. Further, since a catalyst having an oxidizing function is arranged in the engine exhaust passage to oxidize unburned hydrocarbons discharged from the combustion chamber, it is possible to prevent unburned hydrocarbons from being discharged from the internal combustion engine. it can. In addition, when the catalyst temperature is equal to or higher than a predetermined temperature, it is prohibited to perform combustion in which the soot is hardly generated. By the way, when the combustion in which the soot is hardly generated is performed, the unburned hydrocarbon which is in a state before the soot is generated is generated instead of the soot being hardly generated. This unburned hydrocarbon is oxidized by a catalyst disposed in the engine exhaust passage, and at this time, the temperature of the catalyst is increased by reaction heat. Therefore, as described above, in the internal combustion engine according to the first aspect, when the catalyst temperature is equal to or higher than a predetermined temperature, the combustion in which the soot is hardly generated is prohibited. As a result, it is possible to prevent the catalyst temperature from rising excessively.

According to the second aspect of the present invention, as the amount of the inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and is supplied to the combustion chamber. When the amount of the inert gas is further increased, the temperature of the fuel during combustion in the combustion chamber and the temperature of the surrounding gas become lower than the temperature at which soot is generated, and soot is hardly generated. It is possible to perform combustion in which the amount of inert gas supplied into the combustion chamber is larger than the amount of inert gas at which the generation amount of the peak is peak, and soot is hardly generated,
A catalyst having an oxidizing function disposed in an engine exhaust passage to oxidize unburned hydrocarbons discharged from the combustion chamber, and a catalyst temperature detecting means for detecting a temperature of the catalyst, An internal combustion engine is provided in which the air-fuel ratio is shifted to a lean side when combustion is being performed in which little soot is generated and the catalyst temperature is equal to or higher than a predetermined temperature.

In the internal combustion engine according to the second aspect, the amount of the inert gas supplied into the combustion chamber is larger than the amount of the inert gas at which the generation amount of soot becomes a peak, and the combustion at which soot is hardly generated is performed at a low temperature. Since it can be carried out below, it is possible to simultaneously prevent the emission of soot and the emission of NOx from the internal combustion engine. Further, since a catalyst having an oxidizing function is arranged in the engine exhaust passage to oxidize unburned hydrocarbons discharged from the combustion chamber, it is possible to prevent unburned hydrocarbons from being discharged from the internal combustion engine. it can. In addition, the air-fuel ratio is shifted to the lean side when the combustion in which the soot is hardly generated is performed and the catalyst temperature is equal to or higher than a predetermined temperature. By the way, when the combustion in which the soot is hardly generated is performed, the unburned hydrocarbon which is in a state before the soot is generated is generated instead of the soot being hardly generated. This unburned hydrocarbon is oxidized by a catalyst disposed in the engine exhaust passage, and at this time, the temperature of the catalyst is increased by reaction heat. Therefore, as described above, in the internal combustion engine according to claim 1, when the combustion in which the soot is hardly generated is performed and the catalyst temperature is equal to or higher than a predetermined temperature, the air-fuel ratio is shifted to the lean side. Will be shifted. As a result, the amount of unburned hydrocarbons flowing into the catalyst decreases, and therefore, it is possible to prevent the catalyst temperature from excessively increasing.

According to the third aspect of the invention, when the combustion in which the soot is hardly generated is performed and the catalyst temperature is equal to or higher than a predetermined temperature, the air-fuel ratio is shifted to the lean side. An internal combustion engine according to claim 2, wherein the shift is performed in a stepwise manner.

In the internal combustion engine according to the third aspect, when the combustion in which the soot is hardly generated is performed and the catalyst temperature is equal to or higher than a predetermined temperature, the air-fuel ratio is stepped toward the lean side. Is shifted to By the way, if the air-fuel ratio is gradually shifted to the lean side during the combustion in which the soot is hardly generated, it passes through a point where the amount of generated soot becomes a peak. Therefore, as described above, in the internal combustion engine according to the third aspect, the air-fuel ratio is shifted stepwise to the lean side when the combustion in which the soot is hardly generated is performed. Therefore, it is possible to avoid an increase in the amount of soot generated while the air-fuel ratio is shifted to the lean side.

According to the fourth aspect of the present invention, as the amount of the inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and is supplied to the combustion chamber. When the amount of the inert gas is further increased, the temperature of the fuel during combustion in the combustion chamber and the temperature of the surrounding gas become lower than the temperature at which soot is generated, and soot is hardly generated. It is possible to perform combustion in which the amount of inert gas supplied into the combustion chamber is larger than the amount of inert gas at which the generation amount of the peak is peak, and soot is hardly generated,
A catalyst having an oxidizing function disposed in an engine exhaust passage to oxidize unburned hydrocarbons discharged from the combustion chamber, and a catalyst temperature detecting means for detecting a temperature of the catalyst, There is provided an internal combustion engine in which the operating range of an engine capable of performing combustion in which little soot is generated is reduced as the catalyst temperature increases.

In the internal combustion engine according to the fourth aspect, the amount of the inert gas supplied into the combustion chamber is larger than the amount of the inert gas at which the generation amount of soot is a peak, and the combustion at which the soot is hardly generated is performed at a low temperature. Since it can be carried out below, it is possible to simultaneously prevent the emission of soot and the emission of NOx from the internal combustion engine. Further, since a catalyst having an oxidizing function is arranged in the engine exhaust passage to oxidize unburned hydrocarbons discharged from the combustion chamber, it is possible to prevent unburned hydrocarbons from being discharged from the internal combustion engine. it can. In addition, the operating range of the engine capable of performing the combustion in which the soot is hardly generated is reduced as the catalyst temperature increases.
By the way, when the combustion in which the soot is hardly generated is performed, the unburned hydrocarbon which is in a state before the soot is generated is generated instead of the soot being hardly generated. This unburned hydrocarbon is oxidized by a catalyst disposed in the engine exhaust passage, and at this time, the temperature of the catalyst is increased by reaction heat.
That is, in order to prevent the catalyst temperature from excessively rising, it is necessary to prevent the combustion in which the soot is hardly generated when the catalyst temperature is high. Therefore, as described above, in the internal combustion engine according to the fourth aspect, the operating range of the engine capable of performing the combustion that generates little soot is reduced as the catalyst temperature increases. As a result, when the catalyst temperature is high, combustion in which the soot is hardly generated is not performed, and therefore, it is possible to prevent the catalyst temperature from excessively increasing.

According to the fifth aspect of the present invention, the operating range of the engine capable of performing the combustion in which the soot is hardly generated becomes larger as the load and the rotation speed are higher in accordance with the catalyst temperature. An internal combustion engine according to claim 4 is provided.

[0020] In the internal combustion engine according to the fifth aspect, the operating range of the engine capable of performing the combustion in which the soot is hardly generated is increased as the load and the rotation speed are increased in accordance with the catalyst temperature. . By the way, the amount of fuel supplied to the combustion chamber increases as the load and rotation speed increase. Therefore, the generation amount of unburned hydrocarbon also increases as the load and the rotation speed increase. That is, the degree to which the temperature of the catalyst rises increases as the load and the rotation speed increase. Therefore, as described above, in the internal combustion engine according to the fifth aspect, the operating range of the engine capable of performing the combustion in which the soot is hardly generated is larger as the load and the rotation speed are higher, the range being reduced according to the catalyst temperature. Is done. Therefore, it is possible to prevent the catalyst temperature from rising excessively.

According to the invention of claim 6, the internal combustion engine according to any one of claims 1, 2 and 4, wherein the catalyst comprises at least one of an oxidation catalyst, a three-way catalyst and a NOx absorbent. Agencies are provided.

In the internal combustion engine according to the sixth aspect, it is possible to prevent unburned hydrocarbons from being discharged from the internal combustion engine by selecting an appropriate catalyst.

According to the seventh aspect of the present invention, there is provided an exhaust gas recirculation device for recirculating exhaust gas discharged from the combustion chamber into an engine intake passage, wherein the inert gas is supplied to the engine intake passage. An internal combustion engine according to any one of claims 1, 2 and 4, comprising recirculated exhaust gas recirculated therein.

[0024] In the internal combustion engine according to the seventh aspect, the recirculated exhaust gas recirculated into the engine intake passage by the exhaust gas recirculation device is used as the inert gas, so that the inert gas is externally introduced into the combustion chamber. It is possible to avoid the necessity of specially providing a means for supplying the.

According to the eighth aspect of the present invention, the amount of recirculated exhaust gas supplied into the combustion chamber is larger than the amount of recirculated exhaust gas at which the amount of generated soot becomes a peak, and soot is hardly generated. Switching means for selectively switching between the first combustion and the second combustion in which the amount of recirculated exhaust gas supplied into the combustion chamber is smaller than the amount of recirculated exhaust gas at which the generation amount of soot is peaked; The method according to claim 7, further comprising the step of changing the exhaust gas recirculation rate in a stepwise manner when switching from the first combustion to the second combustion or from the second combustion to the first combustion. An internal combustion engine as described is provided.

In the internal combustion engine according to the present invention, when the first combustion is switched from the first combustion to the second combustion or from the second combustion to the first combustion, the exhaust gas recirculation rate is changed stepwise. Accordingly, it is possible to prevent the exhaust gas recirculation rate from being set to the exhaust gas recirculation rate at which the generation amount of soot becomes a peak.

According to the ninth aspect of the present invention, the first
The exhaust gas recirculation rate when the combustion of
9. The internal combustion engine according to claim 8, wherein the internal combustion engine has an exhaust gas recirculation rate of not less than 5 percent and not more than 50 percent when the second combustion is performed.

[0028] In the internal combustion engine according to the ninth aspect, the exhaust gas recirculation rate during the first combustion is made approximately 55% or more, and the exhaust gas is produced when the second combustion is performed. By setting the recirculation rate to approximately 50% or less, it is possible to prevent the exhaust gas recirculation rate from being set to the exhaust gas recirculation rate at which the amount of generated soot reaches a peak.

According to the tenth aspect of the present invention, the operating range of the engine is set to the first operating range on the low load side and the second operating range on the high load side.
9. The internal combustion engine according to claim 8, wherein the internal combustion engine is divided into a first operating region and the first combustion is performed in the first operating region, and the second combustion is performed in the second operating region. Is done.

[0030] In the internal combustion engine according to the tenth aspect, when the first combustion can be performed, that is, when the temperature of the fuel and the surrounding gas during combustion in the combustion chamber can be maintained lower than the soot generation temperature. However, the first combustion is performed in the first operating region on the low load side and the second combustion is performed in the second operating region on the high load side because the heat generation amount due to the combustion is limited to the low load operation in the engine. 2 is performed. Therefore, appropriate combustion can be performed according to the operation range.

[0031]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a first embodiment in which the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3
Is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9
Denotes an exhaust valve, and 10 denotes an exhaust port. Intake port 8
Is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a supercharger, for example, an outlet of a compressor 16 of an exhaust turbocharger 15 via an intake duct 13 and an intercooler 14. .
An inlet of the compressor 16 is connected to an air cleaner 18 via an air suction pipe 17, and a throttle valve 20 driven by a step motor 19 is arranged in the air suction pipe 17. The air suction pipe 1 upstream of the throttle valve 20
A mass flow rate detector 21 for detecting a mass flow rate of the intake air is disposed in the inside 7.

On the other hand, the exhaust port 10 is connected to the exhaust manifold 2.
The exhaust turbine 2 of the exhaust turbocharger 15 via the
3 and an outlet of the exhaust turbine 23 is connected via an exhaust pipe 24 to a catalytic converter 26 having a built-in catalyst 25 having an oxidizing function. Exhaust manifold 22
Inside, an air-fuel ratio sensor 27 is arranged. A temperature sensor 53 for detecting the temperature of the exhaust gas passing through the catalyst 25 is disposed in the exhaust pipe 28 on the downstream side of the catalyst 25, and an output signal of the temperature sensor 53 is output via a corresponding AD converter 47. It is input to the input port 45. The catalyst temperature is estimated based on the output value of the temperature sensor 53. In a modification of the present embodiment, instead of disposing the temperature sensor 53 in the exhaust pipe 28, a temperature sensor is attached to the carrier of the catalyst 25, and the temperature sensor is connected to the carrier temperature (bed temperature) or the exhaust gas temperature. May be used to estimate the catalyst temperature. In this specification, the catalyst temperature refers to the temperature of the catalyst estimated from the temperature of the exhaust gas or the temperature of the carrier.

Returning to the description of this embodiment, the exhaust pipe 28 connected to the outlet of the catalytic converter 26 and the throttle valve 2
The exhaust gas recirculation (hereinafter referred to as E)
(Referred to as GR) through a passage 29, and
E driven by a step motor 30 is provided in the passage 29.
A GR control valve 31 is provided. In the EGR passage 29, an intercooler 32 for cooling the EGR gas flowing in the EGR passage 29 is arranged. In the embodiment shown in FIG. 1, the engine cooling water is guided into the intercooler 32, and the engine cooling water cools the EGR gas.

On the other hand, the fuel injection valve 6 is connected via a fuel supply pipe 33 to a fuel reservoir, a so-called common rail 34. Fuel is supplied into the common rail 34 from an electric control type variable discharge fuel pump 35, and the fuel supplied into the common rail 34 is supplied to the fuel injection valve 6 through each fuel supply pipe 33. A fuel pressure sensor 36 for detecting the fuel pressure in the common rail 34 is attached to the common rail 34, and the fuel pump 35 is controlled so that the fuel pressure in the common rail 34 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 36. Is controlled.

The electronic control unit 40 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45, An output port 46 is provided. The output signal of the mass flow detector 21 is input to the input port 45 via the corresponding AD converter 47, and the output signals of the air-fuel ratio sensor 27 and the fuel pressure sensor 36 are also input to the input port via the corresponding AD converter 47, respectively. 45 is input. A load sensor 51 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. . Also,
The input port 45 has a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °.
Is connected. The engine speed is calculated based on the output value of the crank angle sensor 52. On the other hand, the output port 46 is connected to the fuel injection valve 6, the throttle valve control step motor 19, the EGR control valve control step motor 30, and the fuel pump 35 via a corresponding drive circuit 48.

FIG. 2 shows the throttle valve 2 when the engine is operating at a low load.
The graph shows changes in output torque and changes in smoke, HC, CO, and NOx emissions when the air-fuel ratio A / F (horizontal axis in FIG. 2) is changed by changing the opening degree and the EGR rate of 0. 7 shows an experimental example. As can be seen from FIG. 2, in this experimental example, the smaller the air-fuel ratio A / F, the higher the EGR rate. When the air-fuel ratio A / F is smaller than the stoichiometric air-fuel ratio (≒ 14.6), the EGR rate is 65% or more.

As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the smoke is reduced when the EGR rate becomes close to 40% and the air-fuel ratio A / F becomes about 30. The generation starts to increase. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke is sharply reduced. When the EGR rate is increased to 65% or more and the air-fuel ratio A / F is around 15.0, the smoke becomes almost zero. . That is, almost no soot is generated. At this time, the output torque of the engine slightly decreases, and N
The generation amount of Ox is considerably reduced. On the other hand, at this time, HC,
The amount of generated CO starts to increase.

FIG. 3A shows a change in the combustion pressure in the combustion chamber 5 when the amount of generated smoke is the largest when the air-fuel ratio A / F is around 21, and FIG. 3B shows the air-fuel ratio A / F. The graph shows the change in the combustion pressure in the combustion chamber 5 when the smoke generation amount is substantially zero when F is around 18. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), in the case of FIG. 3 (B) where the amount of smoke generation is almost zero, FIG.
It can be seen that the combustion pressure is lower than in the case shown in (A).

The following can be said from the experimental results shown in FIGS. That is, first, the air-fuel ratio A / F is 1
FIG. 2 when the smoke generation amount is almost zero at 5.0 or less.
As shown in (2), the generation amount of NOx is considerably reduced. N
The decrease in the amount of generated Ox means that the combustion temperature in the combustion chamber 5 has decreased. Therefore, it can be said that the combustion temperature in the combustion chamber 5 has decreased when little soot is generated. . The same can be said from FIG. That is, in the state shown in FIG. 3B where almost no soot is generated, the combustion pressure is low.
The combustion temperature inside is low.

Second, when the amount of generated smoke, that is, the amount of generated soot becomes substantially zero, as shown in FIG.
Emissions increase. This means that hydrocarbons are emitted without growing to soot. That is, the linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 4 are thermally decomposed when the temperature is increased in a state of lack of oxygen, soot precursors are formed, and then mainly, Soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot production process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon as shown in FIG. It will grow to soot. Therefore, as described above, when the amount of generated soot becomes substantially zero, the emission amounts of HC and CO increase as shown in FIG. 2, but HC at this time is a precursor of soot or a hydrocarbon in a state before it. .

The above considerations based on the experimental results shown in FIGS. 2 and 3 can be summarized as follows. When the combustion temperature in the combustion chamber 5 is low, the amount of soot generation becomes almost zero. Is discharged from the combustion chamber 5. As a result of further detailed experimental study on this, if the temperature of the fuel and the surrounding gas in the combustion chamber 5 is lower than a certain temperature, the growth process of the soot is stopped halfway, that is, the soot is It was found that no soot was generated, and soot was generated when the temperature of the fuel and its surroundings in the combustion chamber 5 exceeded a certain temperature.

The temperature of the fuel and its surroundings when the process of producing hydrocarbons is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature, depends on various factors such as the type of fuel and the compression ratio of the air-fuel ratio. Although it cannot be said how many times the temperature changes, this certain temperature has a deep relationship with the amount of generated NOx. Therefore, this certain temperature can be defined to some extent from the amount of generated NOx. it can. That is, as the EGR rate increases, the temperature of the fuel during combustion and the gas temperature around it decrease, and the amount of generated NOx decreases. At this time, when the generation amount of NOx becomes about 10 p.pm or less, soot is hardly generated. Therefore, the above certain temperature is NO
The temperature almost coincides with the temperature when the amount of generated x is about 10 p.pm or less.

Once soot has been produced, it cannot be purified by post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in a state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Considering the post-treatment with a catalyst having an oxidation function as described above, it is extremely difficult to discharge hydrocarbons from the combustion chamber 5 in the state of a precursor of soot or in the state before the soot or in the form of soot from the combustion chamber 5. There is a big difference. The new combustion system employed in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a soot precursor or previous state without producing soot in the combustion chamber 5 and removes the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function.

Now, in order to stop the growth of hydrocarbons before the soot is generated, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 are set to a temperature lower than the temperature at which the soot is generated. It needs to be suppressed. In this case, it has been found that the endothermic effect of the gas around the fuel when the fuel burns has an extremely large effect on suppressing the temperature of the fuel and the gas around the fuel.

That is, if there is only air around the fuel, the evaporated fuel immediately reacts with oxygen in the air and burns. In this case, the temperature of the air separated from the fuel does not rise so much, and only the temperature around the fuel becomes extremely high locally. That is, at this time, the air separated from the fuel hardly absorbs the heat of combustion heat of the fuel. In this case, since the combustion temperature becomes extremely high locally, the unburned hydrocarbons that have received the heat of combustion will generate soot.

On the other hand, the situation is slightly different when fuel is present in a mixed gas of a large amount of inert gas and a small amount of air.
In this case, the fuel vapor diffuses to the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, the combustion temperature is not increased so much because the combustion heat is absorbed by the surrounding inert gas. That is, the combustion temperature can be kept low. That is, the presence of the inert gas plays an important role in suppressing the combustion temperature, and the combustion temperature can be kept low by the endothermic effect of the inert gas.

In this case, in order to suppress the temperature of the fuel and the surrounding gas to a temperature lower than the temperature at which the soot is formed, an amount of the inert gas is required to absorb a sufficient amount of heat to do so. . Therefore, if the fuel amount increases, the required amount of inert gas increases accordingly. In this case, as the specific heat of the inert gas increases, the endothermic effect becomes stronger. Therefore, the inert gas preferably has a higher specific heat. In this regard, it can be said that it is preferable to use EGR gas as the inert gas since CO ₂ and EGR gas have relatively large specific heats.

FIG. 5 shows the relationship between the EGR rate and smoke when EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 5, a curve A indicates that the EGR gas temperature is substantially 9
Curve B shows the case where the EGR gas is cooled by a small cooling device, and curve C shows the case where the temperature is maintained at 0 ° C.
Indicates a case where the EGR gas is not forcibly cooled.

As shown by the curve A in FIG. 5, when the EGR gas is intensely cooled, the amount of soot generation reaches a peak when the EGR rate is slightly lower than 50%. Above a percentage, little soot is generated.

On the other hand, as shown by the curve B in FIG.
When the R gas is cooled slightly, the amount of soot generation peaks when the EGR rate is slightly higher than 50%,
In this case, if the EGR rate is set to about 65% or more, almost no soot is generated.

As shown by the curve C in FIG.
When the R gas is not forcibly cooled, the EGR rate becomes 5
The soot generation amount peaks near 5%, and in this case, if the EGR rate is set to approximately 70% or more, soot is hardly generated.

FIG. 5 shows the amount of smoke generated when the engine load is relatively high. When the engine load is small, the EGR rate at which the amount of soot peaks slightly decreases and almost no soot is generated. The lower limit of the EGR rate to be eliminated also slightly decreases. As described above, the lower limit of the EGR rate at which almost no soot is generated varies depending on the degree of cooling of the EGR gas and the engine load.

FIG. 6 shows a mixture of EGR gas and air necessary to make the temperature of fuel during combustion and the surrounding gas temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas. It shows the gas amount, the ratio of air in the mixed gas amount, and the ratio of EGR gas in the mixed gas. In FIG. 6, the vertical axis indicates the total intake gas amount sucked into the combustion chamber 5, and the dashed line Y indicates the total intake gas amount that can be sucked into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis indicates the required load.

Referring to FIG. 6, the proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air necessary to completely burn the injected fuel. That is, in the case shown in FIG. 6, the ratio between the air amount and the injected fuel amount is the stoichiometric air-fuel ratio. On the other hand, in FIG. 6, the ratio of the EGR gas, that is, the amount of the EGR gas in the mixed gas, is set so that when the injected fuel is burned, the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is formed. The required minimum EGR gas amount is shown. This EGR gas amount is approximately 55% or more in terms of the EGR rate, and is 70% or more in the embodiment shown in FIG. That is, the total intake gas amount sucked into the combustion chamber 5 is represented by a solid line X in FIG. 6, and the ratio between the air amount and the EGR gas amount in the total intake gas amount X is as shown in FIG. The temperature of the fuel and the gas around it will be lower than the temperature at which soot is produced, so that no soot is generated. At this time, NOx
The amount generated is around 10 p.pm or less, and therefore the amount of NOx generated is extremely small.

When the fuel injection amount increases, the amount of heat generated when the fuel burns increases. Therefore, in order to maintain the temperature of the fuel and the surrounding gas at a temperature lower than the temperature at which the soot is generated, the heat generated by the EGR gas is required. Must be increased. Therefore, as shown in FIG. 6, the EGR gas amount must be increased as the injected fuel amount increases.
That is, the EGR gas amount needs to increase as the required load increases.

When the supercharging is not performed, the upper limit of the total intake gas amount X sucked into the combustion chamber 5 is Y. Therefore, in FIG. 6, in the region where the required load is larger than Lo, the required load is reduced. As the ratio increases, the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio unless the EGR gas ratio is reduced. In other words, when the supercharging is not performed and the required air-fuel ratio is maintained at the stoichiometric air-fuel ratio in an area where the required load is larger than Lo, the EGR rate decreases as the required load increases, and In the region where the required load is larger than Lo, the temperature of the fuel and the surrounding gas cannot be maintained at a temperature lower than the temperature at which soot is generated.

However, as shown in FIG. 1, when the EGR gas is recirculated through the EGR passage 29 into the inlet side of the supercharger, that is, into the air suction pipe 17 of the exhaust turbocharger 15, the region where the required load is larger than Lo is obtained. In EGR rate 5
It can be maintained at 5% or more, for example 70%, so that the temperature of the fuel and its surrounding gas can be kept below the temperature at which soot is produced. That is, if the EGR gas is recirculated so that the EGR rate in the air suction pipe 17 becomes, for example, 70%, the EGR rate of the suction gas boosted by the compressor 16 of the exhaust turbocharger 15 also becomes 70%. The temperature of the fuel and the surrounding gas can be maintained at a temperature lower than the temperature at which soot is generated, to the extent that the pressure can be increased by the compressor 16. Therefore, the operating range of the engine that can generate low-temperature combustion can be expanded. When the EGR rate is set to 55% or more in a region where the required load is larger than Lo, E
The throttle valve 20 is opened when the GR control valve 31 is fully opened.
Is slightly closed.

As described above, FIG. 6 shows the case where the fuel is burned under the stoichiometric air-fuel ratio. However, even if the air amount is smaller than the air amount shown in FIG. 6, that is, the air-fuel ratio is made rich. Even so, while suppressing the generation of soot, the generation amount of NOx was reduced to 10 p.p.
m or less, and even if the air amount is larger than the air amount shown in FIG. 6, that is, even if the average value of the air-fuel ratio is 17 to 18 lean, soot generation is prevented. Meanwhile, the amount of generated NOx can be reduced to about 10 p.pm or less.

That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the excess fuel does not grow into soot, and soot is generated. There is no. At this time, only a very small amount of NOx is generated. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated if the combustion temperature increases, but in the present invention, the soot is suppressed to a low temperature, so that the soot is reduced. Not generated at all. Furthermore, NOx
Only very small amounts are generated.

As described above, when low-temperature combustion is performed, soot is generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean. However, the generation amount of NOx becomes extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time.

By the way, the temperature of the fuel and its surrounding gas during combustion in the combustion chamber can be suppressed below the temperature at which the growth of hydrocarbons stops halfway, only when the engine is under low load operation where the calorific value due to combustion is relatively small. Can be Therefore, in the embodiment according to the present invention, during the low load operation in the engine, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas around it to a temperature below the temperature at which the growth of hydrocarbons stops halfway. In addition, the second combustion, that is, the combustion that is usually performed conventionally, is performed during the high load operation of the engine. Here, the first combustion, that is, the low-temperature combustion, has a larger amount of the inert gas in the combustion chamber than the amount of the inert gas at which the soot generation amount is at a peak, as is clear from the description so far. The second combustion, that is, the combustion that has been performed normally in the past, is a combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of soot is peaked. Say that.

FIG. 7 shows a first operation region I in which the first combustion, that is, low-temperature combustion is performed, and a second operation region II in which the second combustion, that is, combustion by the conventional combustion method, is performed. I have. In FIG. 7, the vertical axis L indicates the amount of depression of the accelerator pedal 50, that is, the required load, and the horizontal axis N indicates the engine speed. In FIG. 7, X (N) is the first
Shows the first boundary between the operating region I and the second operating region II, and Y (N) represents the first operating region I and the second operating region.
2 shows a second boundary with II. The determination of the change of the operating range from the first operating range I to the second operating range II is made based on the first boundary X (N), and the determination of the change from the second operating range II to the first
The determination of the change of the operation region to the operation region I of the second boundary Y
(N).

That is, when the operating state of the engine is in the first operating region I
When the required load L exceeds a first boundary X (N), which is a function of the engine speed N, during low-temperature combustion, it is determined that the operation region has shifted to the second operation region II, Combustion is performed by a conventional combustion method. Next, when the required load L becomes lower than a second boundary Y (N) which is a function of the engine speed N, it is determined that the operation region has shifted to the first operation region I, and low-temperature combustion is performed again.

As described above, two boundaries, that is, the first boundary X (N) and the second boundary Y (N) on the lower load side than the first boundary X (N) are provided are as follows. For three reasons. The first reason is that the combustion temperature is relatively high on the high load side of the second operation region II, and even if the required load L becomes lower than the first boundary X (N), low-temperature combustion cannot be performed immediately. Because. That is, the low-temperature combustion does not immediately start unless the required load L becomes considerably low, that is, when the required load L becomes lower than the second boundary Y (N). The second reason is that hysteresis is provided for a change in the operation range between the first operation range I and the second operation range II.

By the way, when the operating region of the engine is in the first operating region I and low-temperature combustion is being performed, soot is hardly generated, and the unburned hydrocarbon is replaced with the precursor of soot or the state before it. It is discharged from the combustion chamber 5 in the form. At this time, the unburned hydrocarbon discharged from the combustion chamber 5 is oxidized well by the catalyst 25 having an oxidizing function.

As the catalyst 25, an oxidation catalyst, a three-way catalyst, or a NOx absorbent can be used. When the average air-fuel ratio in the combustion chamber 5 is lean, the NOx absorbent
And has the function of releasing NOx when the average air-fuel ratio in the combustion chamber 5 becomes rich.

This NOx absorbent uses, for example, alumina as a carrier and, for example, potassium K, sodium N
a, lithium Li, at least one selected from alkali metals such as cesium Cs, alkaline earths such as barium Ba and calcium Ca, rare earths such as lanthanum La and yttrium Y, and noble metals such as platinum Pt. Is carried.

In addition to the oxidation catalyst, the three-way catalyst and the NO
The x absorbent also has an oxidizing function, and thus the three-way catalyst and the NOx absorbent can be used as the catalyst 25 as described above.

FIG. 8 shows the output of the air-fuel ratio sensor 27. As shown in FIG. 8, the output current I of the air-fuel ratio sensor 27 changes according to the air-fuel ratio A / F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 27.

Next, operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG. FIG. 9 shows the throttle valve 2 with respect to the required load L.
0 indicates the opening degree, the opening degree of the EGR control valve 31, the EGR rate, the air-fuel ratio, the injection timing, and the injection amount. As shown in FIG. 9, in the first operating region I where the required load L is low, the opening of the throttle valve 20 is gradually increased from almost fully closed to about 2/3 opening as the required load L increases. E
The degree of opening of the GR control valve 31 is gradually increased from almost fully closed to fully open as the required load L increases. Also,
In the example shown in FIG. 9, in the first operation region I, the EGR rate is set to approximately 70%, and the air-fuel ratio is set to a slightly lean air-fuel ratio.

In other words, in the first operation region I, the EGR
The opening of the throttle valve 20 and the opening of the EGR control valve 31 are controlled such that the rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. In the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS is delayed as the required load L is increased, and the injection completion timing θE is delayed as the injection start timing θS is delayed.

During idle operation, the throttle valve 2
0 is closed to almost fully closed, and at this time, the EGR control valve 31
Is also closed to near full closure. When the throttle valve 20 is closed close to the fully closed state, the pressure in the combustion chamber 5 at the start of compression decreases, so that the compression pressure decreases. When the compression pressure decreases, the compression work by the piston 4 decreases, so that the vibration of the engine body 1 decreases. That is, during idling operation, the throttle valve 2
0 is closed until it is almost fully closed.

On the other hand, the operating range of the engine is the first operating range I
From the second operating region II to the second operating region II, the opening of the throttle valve 20 is increased stepwise from about 2/3 opening toward the full opening direction. At this time, in the example shown in FIG. 9, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. That is, the EGR rate at which the EGR rate generates a large amount of smoke
The engine operating range is the first because it jumps over the rate range (Fig. 5).
A large amount of smoke does not occur when changing from the operating region I to the second operating region II.

In the second operation region II, the conventional combustion is performed. In the second operating region II, the throttle valve 20 is held in a fully open state except for a part, and the opening of the EGR control valve 31 is gradually reduced as the required load L increases. In this operating region II, the EGR rate decreases as the required load L increases, and the air-fuel ratio decreases as the required load L increases. However, the air-fuel ratio is a lean air-fuel ratio even when the required load L increases. In the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

FIG. 10A shows the target air-fuel ratio A / F in the first operation region I. In FIG. 10A, A / F = 15.5, A / F = 16, A / F = 17,
Each curve represented by A / F = 18 has a target air-fuel ratio of 1
5.5, 16, 17, and 18, and the air-fuel ratio between the curves is determined by proportional distribution. FIG.
As shown in (A), the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the target air-fuel ratio A / F becomes leaner as the required load L decreases.

That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, low-temperature combustion can be performed even if the EGR rate is reduced as the required load L decreases.
When the EGR rate is reduced, the air-fuel ratio increases. Therefore, as shown in FIG. 10A, as the required load L decreases, the target air-fuel ratio A / F increases. Target air-fuel ratio A /
As F increases, the fuel consumption rate increases. Accordingly, in order to make the air-fuel ratio as lean as possible, in the embodiment according to the present invention, the target air-fuel ratio A / F is increased as the required load L decreases.

Note that the target air-fuel ratio A / F shown in FIG. 10A is stored in advance in the ROM 4 as a function of the required load L and the engine speed N as shown in FIG.
2 is stored. Also, the throttle valve 2 required to set the air-fuel ratio to the target air-fuel ratio A / F shown in FIG.
The target opening ST of 0 is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG.
EGR required to achieve target air-fuel ratio A / F shown in (A)
As shown in FIG. 11B, the target opening SE of the control valve 31 is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N.

FIG. 12A shows the target air-fuel ratio A when the second combustion, that is, the normal combustion by the conventional combustion method is performed.
/ F. Note that A / F in FIG.
= 24, A / F = 35, A / F = 45, and A / F = 60 indicate target air-fuel ratios of 24, 35, 45, and 6, respectively.
0 is shown. The target air-fuel ratio A shown in FIG.
/ F is a function of the required load L and the engine speed N as shown in FIG.
Is stored within. Also, the throttle valve 20 required to set the air-fuel ratio to the target air-fuel ratio A / F shown in FIG.
The target opening ST is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG.
As shown in FIG. 13 (B), the target opening degree SE of the EGR control valve 31 required to obtain the target air-fuel ratio A / F shown in FIG. It is stored in the ROM 42.

When the second combustion is being performed, the fuel injection amount Q is calculated based on the required load L and the engine speed N. The fuel injection amount Q is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG.

Next, the operation control of this embodiment will be described with reference to FIGS. Referring to FIGS. 15 and 16, first, at step 100, it is determined whether or not the catalyst temperature T is equal to or higher than a predetermined temperature T '. If NO, proceed to step 101, and if YES, proceed to step 111 to perform the second
Is performed. In step 101, it is determined whether or not a flag I indicating that the operating state of the engine is in the first operating region I is set. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 102, where the required load L is set to the first operating range.
Is determined to be larger than the boundary X (N). When L ≦ X (N), the routine proceeds to step 106, where low-temperature combustion is performed. On the other hand, in step 102, L>
When it is determined that X (N) has been reached, step 103
And the flag I is reset.
Proceeding to 1, the second combustion is performed.

In step 101, it is determined that the flag I indicating that the operation state of the engine is in the first operation area I is not set, that is, the operation state of the engine is in the second operation area II. In some cases, the routine proceeds to step 104, where it is determined whether the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), the routine proceeds to step 111, where the second combustion is performed under a lean air-fuel ratio. On the other hand, when it is determined in step 104 that L <Y (N), the routine proceeds to step 105, where the flag I is set, and then proceeds to step 106 to perform low-temperature combustion.

In step 106, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG.
The opening of the throttle valve 20 is set to the target opening ST.
Next, at step 107, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening of the control valve 31 is set as the target opening SE. Next, at step 108, the mass flow rate of the intake air detected by the mass flow rate detector 21 (hereinafter, simply referred to as the intake air amount).
Ga is captured, and then in step 109, FIG.
The target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 110, based on the intake air amount Ga and the target air-fuel ratio A / F, a fuel injection amount Q necessary for setting the air-fuel ratio to the target air-fuel ratio A / F is calculated.

When the required load L or the engine speed N changes during low-temperature combustion, the opening of the throttle valve 20 and the opening of the EGR control valve 31 immediately change to the required load L and the engine speed N. Target opening ST according to
Matched to SE. Therefore, for example, when the required load L is increased, the amount of air in the combustion chamber 5 is immediately increased, and the generated torque of the engine is immediately increased.

On the other hand, the opening degree of the throttle valve 20 or the EGR
When the opening degree of the control valve 31 changes and the intake air amount changes, the change in the intake air amount Ga is detected by the mass flow rate detector 21, and the fuel injection amount Q is controlled based on the detected intake air amount Ga. Is done. That is, the fuel injection amount Q is changed after the intake air amount Ga actually changes.

In step 111, the target fuel injection amount Q is calculated from the map shown in FIG. 14, and the fuel injection amount is set as the target fuel injection amount Q. Next, at step 112, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. Next, at step 113, FIG.
The target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 3 (B), and the opening of the EGR control valve 31 is set as the target opening SE.

Next, at step 114, the intake air amount Ga detected by the mass flow detector 21 is taken. Next, at step 115, the fuel injection amount Q and the intake air amount Ga
From this, the actual air-fuel ratio (A / F) _R is calculated. Next, at step 116, the target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 117, it is determined whether or not the actual air-fuel ratio (A / F) _R is larger than the target air-fuel ratio A / F. (A / F) If _R > A / F, the routine proceeds to step 118, where the throttle opening correction value ΔS
T is reduced by a constant value α, then step 12
Go to 0. On the other hand, when (A / F) _R ≤A / F, the routine proceeds to step 119, where the correction value ΔST is increased by a constant value α, and then the routine proceeds to step 120. In step 120, the final target opening ST is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20, and the opening of the throttle valve 20 is used as the final target opening ST. That is, the opening of the throttle valve 20 is controlled so that the actual air-fuel ratio (A / F) _R becomes the target air-fuel ratio A / F.

When the required load L or the engine speed N changes during the second combustion, the fuel injection amount immediately matches the target fuel injection amount Q corresponding to the required load L and the engine speed N. I'm sick. For example, the required load L
Is increased, the fuel injection amount is immediately increased, and thus the generated torque of the engine is immediately increased.

On the other hand, when the fuel injection amount Q is increased and the air-fuel ratio deviates from the target air-fuel ratio A / F, the opening of the throttle valve 20 is controlled so that the air-fuel ratio becomes the target air-fuel ratio A / F. That is, the air-fuel ratio is changed after the fuel injection amount Q changes.

In the embodiments described above, the fuel injection amount Q is controlled by the open loop when low-temperature combustion is being performed, and the air-fuel ratio is controlled by the opening degree of the throttle valve 20 when the second combustion is being performed. It is controlled by changing.
However, the fuel injection amount Q can be feedback-controlled based on the output signal of the air-fuel ratio sensor 27 when the low-temperature combustion is being performed, and the air-fuel ratio can be controlled by the EGR control when the second combustion is being performed. The control can also be performed by changing the opening of the valve 31.

According to the present embodiment, the EG at which the soot generation amount reaches a peak in steps 106 to 110
Since the amount of EGR gas supplied into the combustion chamber 5 is larger than the amount of R gas and low-temperature combustion in which little soot is generated can be performed, it is possible to simultaneously discharge soot and NOx from the internal combustion engine. Can be blocked. Further, since the catalyst 25 having an oxidizing function is disposed in the exhaust pipe 28 to oxidize unburned hydrocarbons discharged from the combustion chamber 5, the unburned hydrocarbons are prevented from being discharged from the internal combustion engine. be able to. In addition, when it is determined in step 100 that the catalyst temperature T is equal to or higher than the predetermined temperature T ', execution of low-temperature combustion (steps 106 to 110) is prohibited by proceeding to step 111. Therefore, it is possible to prevent the temperature of the catalyst 25 from rising excessively.

Further, according to the present embodiment, after the low temperature combustion is executed in the previous routine (steps 106 to 110), the catalyst temperature T becomes equal to or higher than the predetermined temperature T 'in step 100 of the current routine. When it is determined that the combustion has been performed, that is, when the low-temperature combustion is being performed and the catalyst temperature T is equal to or higher than the predetermined temperature T ′, the routine proceeds to step 111, whereby the combustion becomes relatively rich. The low-temperature combustion performed under the air-fuel ratio is switched to the second combustion performed under a relatively lean air-fuel ratio, that is, the air-fuel ratio is shifted stepwise toward the lean side. By shifting the air-fuel ratio to the lean side,
The amount of unburned hydrocarbons flowing into the catalyst 25 is reduced, and therefore, it is possible to prevent the temperature of the catalyst 25 from excessively increasing. Further, by shifting the air-fuel ratio in a stepwise manner, it is possible to avoid an increase in the amount of soot generated during the shift of the air-fuel ratio to the lean side.

Next, a second embodiment of the internal combustion engine of the present invention will be described. The configuration of this embodiment is almost the same as the configuration of the first embodiment shown in FIG. FIG. 17 shows the required load L, the catalyst temperature T, the first operation region I, and the second operation region II.
FIG. In the present embodiment, in order to prevent the catalyst temperature from excessively rising, instead of prohibiting the execution of the low-temperature combustion when the catalyst temperature is high as in the first embodiment, the first embodiment in which the low-temperature combustion is executed is performed. The operation region I is reduced according to the catalyst temperature. More specifically, as shown in FIG. 17, the first operation region I is reduced as the catalyst temperature T increases.

FIGS. 18 and 19 are diagrams showing a first operation region I and a second operation region II of the present embodiment. FIG.
8 and FIG. 19, the first boundary X of the present embodiment
(N, T) and the second boundary Y (N, T) are the engine speed N
Not only that, it is changed by the catalyst temperature T. In particular, when the catalyst temperature T increases from T ₁ to T _2, the first operating region I capable of performing low temperature combustion is reduced. Further, the degree to which the first operation region I is reduced increases as the required load L and the engine speed N increase.

Next, the operation control of this embodiment will be described with reference to FIG. Referring to FIG. 20, first, in step 101, it is determined whether or not a flag I indicating that the operating state of the engine is in the first operating region I is set. When the flag I is set,
That is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 200, where the required load L is reduced to the first boundary X.
It is determined whether or not (N, T) (FIG. 18) has become larger. When L ≦ X (N, T), the routine proceeds to step 106, where low-temperature combustion is performed. On the other hand, when it is determined in step 200 that L> X (N, T), the routine proceeds to step 103, where the flag I is reset, and then proceeds to step 111 to perform the second combustion.

In step 101, it is determined that the flag I indicating that the operation state of the engine is in the first operation area I is not set, that is, the operation state of the engine is in the second operation area II. At step 201, it is determined whether the required load L has become lower than the second boundary Y (N, T) (FIG. 19). L ≧ Y (N, T)
In the case of, the routine proceeds to step 111, where the second combustion is performed under the lean air-fuel ratio. On the other hand, when it is determined in step 201 that L <Y (N, T), the routine proceeds to step 105, where the flag I is set, and then proceeds to step 106 to perform low-temperature combustion.

In step 106, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG.
The opening of the throttle valve 20 is set to the target opening ST.
Next, at step 107, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening of the control valve 31 is set as the target opening SE. Next, at step 108, the mass flow rate of the intake air detected by the mass flow rate detector 21 (hereinafter, simply referred to as the intake air amount).
Ga is captured, and then in step 109, FIG.
The target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 110, based on the intake air amount Ga and the target air-fuel ratio A / F, a fuel injection amount Q necessary for setting the air-fuel ratio to the target air-fuel ratio A / F is calculated.

When the required load L or the engine speed N changes during the low-temperature combustion, the opening of the throttle valve 20 and the opening of the EGR control valve 31 immediately change to the required load L and the engine speed N. Target opening ST according to
Matched to SE. Therefore, for example, when the required load L is increased, the amount of air in the combustion chamber 5 is immediately increased, and the generated torque of the engine is immediately increased.

On the other hand, the opening degree of the throttle valve 20 or the EGR
When the opening degree of the control valve 31 changes and the intake air amount changes, the change in the intake air amount Ga is detected by the mass flow rate detector 21, and the fuel injection amount Q is controlled based on the detected intake air amount Ga. Is done. That is, the fuel injection amount Q is changed after the intake air amount Ga actually changes.

In step 111, the target fuel injection amount Q is calculated from the map shown in FIG. 14, and the fuel injection amount is set as the target fuel injection amount Q. Next, at step 112, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. Next, at step 113, FIG.
The target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 3 (B), and the opening of the EGR control valve 31 is set as the target opening SE.

Next, at step 114, the intake air amount Ga detected by the mass flow detector 21 is taken. Next, at step 115, the fuel injection amount Q and the intake air amount Ga
From this, the actual air-fuel ratio (A / F) _R is calculated. Next, at step 116, the target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 117, it is determined whether or not the actual air-fuel ratio (A / F) _R is larger than the target air-fuel ratio A / F. (A / F) If _R > A / F, the routine proceeds to step 118, where the throttle opening correction value ΔS
T is reduced by a constant value α, then step 12
Go to 0. On the other hand, when (A / F) _R ≤A / F, the routine proceeds to step 119, where the correction value ΔST is increased by a constant value α, and then the routine proceeds to step 120. In step 120, the final target opening ST is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20, and the opening of the throttle valve 20 is used as the final target opening ST. That is, the opening of the throttle valve 20 is controlled so that the actual air-fuel ratio (A / F) _R becomes the target air-fuel ratio A / F.

When the required load L or the engine speed N changes during the second combustion, the fuel injection amount immediately matches the target fuel injection amount Q corresponding to the required load L and the engine speed N. I'm sullen. For example, the required load L
Is increased, the fuel injection amount is immediately increased, and thus the generated torque of the engine is immediately increased.

On the other hand, when the fuel injection amount Q is increased and the air-fuel ratio deviates from the target air-fuel ratio A / F, the opening of the throttle valve 20 is controlled so that the air-fuel ratio becomes the target air-fuel ratio A / F. That is, the air-fuel ratio is changed after the fuel injection amount Q changes.

In the embodiments described above, the fuel injection amount Q is controlled by open-loop control during low-temperature combustion, and the air-fuel ratio decreases the opening of the throttle valve 20 during second combustion. It is controlled by changing.
However, the fuel injection amount Q can be feedback-controlled based on the output signal of the air-fuel ratio sensor 27 when the low-temperature combustion is being performed, and the air-fuel ratio can be controlled by the EGR control when the second combustion is being performed. The control can also be performed by changing the opening of the valve 31.

According to this embodiment, the EG at which the soot generation amount reaches a peak in steps 106 to 110
Since the amount of EGR gas supplied into the combustion chamber 5 is larger than the amount of R gas and low-temperature combustion in which little soot is generated can be performed, it is possible to simultaneously discharge soot and NOx from the internal combustion engine. Can be blocked. Further, since the catalyst 25 having an oxidizing function is disposed in the exhaust pipe 28 to oxidize unburned hydrocarbons discharged from the combustion chamber 5, the unburned hydrocarbons are prevented from being discharged from the internal combustion engine. be able to. In addition, the first operating region I in which low-temperature combustion can be performed is reduced as the catalyst temperature T becomes higher as shown in FIGS. As a result, when the catalyst temperature T is high, low-temperature combustion is not performed, and therefore, it is possible to prevent the temperature of the catalyst 25 from excessively increasing.

Further, according to the present embodiment, the amount of fuel supplied to the combustion chamber 5 increases as the required load L and the engine speed N increase, so that the amount of unburned hydrocarbons also decreases with the required load L and the engine speed. In view of the fact that the higher the number N is, that is, the higher the temperature of the catalyst 25 is, the higher the required load L and the engine speed N are, the low-temperature combustion can be performed as shown in FIGS. 18 and 19. In the first operating region I, the region that is reduced in accordance with the catalyst temperature T increases as the required load L and the engine speed N increase. Therefore, it is possible to appropriately prevent the temperature of the catalyst 25 from excessively rising.

[0107]

According to the first and second aspects of the present invention,
Emission of soot (smoke) from the internal combustion engine and NO
While simultaneously preventing x from being discharged, it is possible to prevent unburned hydrocarbons from being discharged from the internal combustion engine and to prevent the catalyst temperature from excessively rising.

According to the third aspect of the invention, it is possible to avoid an increase in the amount of soot generated while the air-fuel ratio is shifted to the lean side.

According to the fourth and fifth aspects of the present invention, soot (smoke) is discharged from the internal combustion engine and NOx
While simultaneously preventing unburned hydrocarbons from being discharged from the internal combustion engine and preventing the catalyst temperature from excessively rising.

According to the sixth aspect of the present invention, it is possible to prevent unburned hydrocarbons from being discharged from the internal combustion engine by selecting an appropriate catalyst.

According to the invention described in claim 7, it is possible to avoid the necessity of specially providing a means for supplying an inert gas from the outside into the combustion chamber.

According to the eighth and ninth aspects of the present invention, it is possible to prevent the exhaust gas recirculation rate from being set to the exhaust gas recirculation rate at which the generation amount of soot becomes a peak.

According to the tenth aspect, appropriate combustion can be performed according to the operation range.

[Brief description of the drawings]

FIG. 1 is an overall view of a compression ignition type internal combustion engine.

FIG. 2 is a diagram showing amounts of smoke and NOx generated;

FIG. 3 is a diagram showing a combustion pressure.

FIG. 4 is a diagram showing fuel molecules.

FIG. 5 is a diagram showing a relationship between a generation amount of smoke and an EGR rate.

FIG. 6 is a diagram showing a relationship between an injected fuel amount and a mixed gas amount.

FIG. 7 shows a first operating region I and a second operating region I of the first embodiment.
FIG. 3 is a diagram showing an operation region II of FIG.

FIG. 8 is a diagram showing an output of an air-fuel ratio sensor.

FIG. 9 is a view showing an opening degree of a throttle valve and the like.

FIG. 10 is a diagram showing an air-fuel ratio and the like in a first operation region I.

FIG. 11 is a diagram showing a map of a target opening degree of a throttle valve and the like.

FIG. 12 is a diagram showing an air-fuel ratio and the like in a second combustion.

FIG. 13 is a view showing a map of a target opening degree of a throttle valve and the like.

FIG. 14 is a diagram showing a map of a fuel injection amount.

FIG. 15 is a flowchart for controlling the operation of the engine of the first embodiment.

FIG. 16 is a flowchart for controlling the operation of the engine of the first embodiment.

FIG. 17 is a diagram showing a relationship between a required load L, an engine speed N, a first operating region I, and a second operating region II.

FIG. 18 is a diagram showing a first operation region I and a second operation region II of the second embodiment.

FIG. 19 is a diagram showing a first operation region I and a second operation region II of the second embodiment.

FIG. 20 is a flowchart for controlling the operation of the engine of the second embodiment.

[Explanation of symbols]

 5 Combustion chamber 6 Fuel injection valve 25 Catalyst 28 Exhaust pipe 29 EGR passage 31 EGR control valve 53 Temperature sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/24 F01N 3/24 R S F02D 21/08 301 F02D 21/08 301B 301D 311 311B 41/02 355 41/02 355 41/04 355 41/04 355 43/00 301 43/00 301N 301E (72) Inventor Masato Goto 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Takekazu Ito 1 Toyota Motor City, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Hiroki Murata 1 Toyota Motor City Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 3G062 AA01 BA02 BA04 BA06 CA06 DA00 EA11 FA08 GA01 GA04 GA05 GA06 GA09 GA15 GA21 3G084 AA01 BA09 BA20 CA03 CA04 CA09 DA10 EB08 FA00 FA07 FA10 FA18 FA29 FA33 FA 38 3G091 AA02 AA10 AA11 AA18 AB02 AB03 AB06 CB02 CB07 CB08 DB10 EA00 EA01 EA02 EA05 EA07 EA18 EA30 EA31 EA34 FB10 FB11 FB12 HA36 HA37 HA39 HB05 HB06 3G092 AA02 AA17 EA18 EA18 EA18 EA04 HC03X HC03Z HD02Z HD05Z HD07X HD07Z HE01Z HE03Z HF08Z 3G301 HA02 HA13 JA24 JA25 JA26 JA33 KA06 KA23 LA00 MA01 NE15 PA01Z PB08Z PD03Z PD12Z PE01Z PE03Z PF03Z

Claims (10)

[Claims] 1. As the amount of inert gas supplied to the combustion chamber increases, the amount of generated soot gradually increases and reaches a peak, and the amount of inert gas supplied to the combustion chamber further increases. As a result, the temperature of the fuel and surrounding gas during combustion in the combustion chamber becomes lower than the temperature at which soot is generated, and almost no soot is generated. The amount of inert gas supplied into the combustion chamber is larger than the amount of gas, so that combustion can be performed in which little soot is generated, and the engine exhaust passage is used to oxidize unburned hydrocarbons discharged from the combustion chamber. A catalyst having an oxidizing function disposed therein and catalyst temperature detecting means for detecting the temperature of the catalyst, and when the catalyst temperature is equal to or higher than a predetermined temperature, the soot is hardly generated. To do the burning Internal combustion engine to be banned. 2. As the amount of inert gas supplied into the combustion chamber increases, the amount of generated soot gradually increases and reaches a peak, and the amount of inert gas supplied into the combustion chamber further increases. As a result, the temperature of the fuel and surrounding gas during combustion in the combustion chamber becomes lower than the temperature at which soot is generated, and almost no soot is generated. The amount of inert gas supplied into the combustion chamber is larger than the amount of gas, so that combustion can be performed in which little soot is generated, and the engine exhaust passage is used to oxidize unburned hydrocarbons discharged from the combustion chamber. A catalyst having an oxidation function disposed therein, and catalyst temperature detecting means for detecting the temperature of the catalyst, wherein the combustion is performed when little soot is generated, and the catalyst temperature is set in advance. Below the specified temperature An internal combustion engine that shifts the air-fuel ratio to the lean side when it is above. 3. The method according to claim 1, wherein the air-fuel ratio is shifted in a stepwise manner toward the lean side when the combustion in which the soot is hardly generated is performed and the catalyst temperature is equal to or higher than a predetermined temperature. Item 3. An internal combustion engine according to item 2. 4. As the amount of inert gas supplied to the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and the amount of inert gas supplied to the combustion chamber further increases. As a result, the temperature of the fuel and surrounding gas during combustion in the combustion chamber becomes lower than the temperature at which soot is generated, and almost no soot is generated. The amount of inert gas supplied into the combustion chamber is larger than the amount of gas, so that combustion can be performed in which little soot is generated, and the engine exhaust passage is used to oxidize unburned hydrocarbons discharged from the combustion chamber. A catalyst having an oxidation function disposed therein, and a catalyst temperature detecting means for detecting a temperature of the catalyst, wherein an operating region of an engine capable of performing combustion in which the soot is hardly generated is formed in a catalyst temperature range. Shrink as hot An internal combustion engine designed to be smaller. 5. The internal combustion engine according to claim 4, wherein the operating range of the engine capable of performing the combustion in which the soot is hardly generated becomes larger as the load and the rotation speed increase as the catalyst temperature increases. 6. The catalyst according to claim 1, wherein said catalyst is an oxidation catalyst, a three-way catalyst or NO.
5. The internal combustion engine according to claim 1, wherein the internal combustion engine comprises at least one x-absorbent. 7. An exhaust gas recirculation device for recirculating exhaust gas discharged from the combustion chamber into an engine intake passage, wherein the inert gas is recirculated into the engine intake passage. The internal combustion engine according to any one of claims 1, 2 and 4, wherein the internal combustion engine is made of gas. 8. The first combustion in which the amount of recirculated exhaust gas supplied into the combustion chamber is larger than the amount of recirculated exhaust gas at which the amount of generated soot becomes a peak, and soot is hardly generated, and the generation of soot Switching means for selectively switching between the second combustion in which the amount of recirculated exhaust gas supplied into the combustion chamber is smaller than the amount of recirculated exhaust gas in which the amount reaches a peak, The internal combustion engine according to claim 7, wherein the exhaust gas recirculation rate is changed stepwise when the second combustion or the second combustion is switched to the first combustion. 9. The exhaust gas recirculation rate during the first combustion is substantially 55% or more, and the exhaust gas recirculation rate during the second combustion is substantially 50%. The internal combustion engine of claim 8, which is less than or equal to percent. 10. An engine operating region is divided into a first operating region on a low load side and a second operating region on a high load side, and the first combustion is performed in the first operating region. The internal combustion engine according to claim 8, wherein the second combustion is performed in a second operation range.